In communications networks, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed.
For example, handover is a vital part of any cellular communications network. A handover may be defined as the process of transferring an ongoing connection of a wireless device from one radio access network node (denoted the serving radio access network node) to another radio access network node (denoted the target radio access network node) in order to accomplish a transparent service over a large coverage area. The handover should be performed without any loss of data transmission to/from the wireless device, and with as small interrupt as possible for the wireless device.
To enable a handover, it is necessary to find a suitable target cell as served by the target radio access network node, and to ensure that it is possible to sustain reliable communication to/from the wireless device in the target cell. Candidates for suitable target radio access network nodes (and/or target cells) are usually stored in so-called neighbor lists, which are stored at least at the serving radio access network node.
For a wireless device (WD) to receive or measure on a target cell (i.e., an area served by a target radio access network (RAN) node), it needs be synchronized with the cell (i.e., with the target node). In legacy systems, all RAN nodes continuously transmit synchronization signals that WDs in neighbor cells use for synchronization with target cell. Examples include, but are not limited to, the synchronization channel (SCH) in Wideband Code Division Multiple Access (WCDMA) based communications networks and the primary and secondary synchronization signals in Long Term Evolution (LTE) based communications networks. The synchronization is usually achieved by correlating the received signal with a known signal; in LTE the correlation may be performed in both time and frequency domain. The synchronization procedure is often dived into several steps where the frequency and time resolution and is improved for each step. For time synchronization, the steps may include finding symbol, slot and frame timing.
Future cellular communications networks may use advanced antenna systems to a large extent. With such antennas, signals will be transmitted in narrow transmission beams to increase signal strength in some directions, and/or to reduce interference in other directions. When the antenna is used to increase coverage, handover between narrow transmission beams in neighboring RAN nodes may become a necessity. The serving RAN node also needs to decide if a beam switch or beam update is necessary within the own cell. The transmission beam through which the RAN node is currently communicating with the WD is called the serving beam and the transmission beam it will hand over to, or switch to, is called the target beam. The serving beam and the target beam may be transmission beams of the same or different RAN node.
In a cellular system with an advanced antenna system that uses narrow beams, beam updates for a WD might recur quite often. To synchronize and measure on the different candidate beams, the WD must thus potentially perform extensive timing synchronization procedures, especially in non-synchronized networks. For the WD, the synchronization procedure may be quite complex, since it may need to measure on many transmission beams at once.
Hence, there is still a need for improved handling of mobility synchronization measurements.